The macromolecules comprising neural structures are constructed and assembled according to genetic information. Our objective is to study how genes control the structure and function of the nervous system. Behavioral mutants are isolated in Drosophila melanogaster including those that are conditional paralytic mutants. These are characterized beaviorally and genetically. Intracellular recordings are performed on larval muscle to identify and analyze those mutants with defects in nerve conduction, neuromuscular transmission, or muscle response. Among those mutants that we have been studying are those that block the propagation of action potential (e.g. nap ts, para ts) and those that cause repetitive firing of action potentials (e.g., Sh, bas MW1). Functional relationships among the various gene products comprising neuronal membranes are studied by examining epistatic and suppressive interactions in double mutants. Isolation of additonal mutants is being carried out to further extend our spectrum of genetic modifications of membrane excitability. This analysis establishes a framework for the eventual identification of the molecular components of the nervous system and may provide a better understanding of the underlying defect in certain heritable neurological disorders in humans.